In recent years, the rare earth magnet such as an R—Fe—B based magnet (R means a rare earth element such as Nd) has been developed as a permanent magnet presenting a high energy of a 25 or higher MGOe product. For instance, patent document 1 and patent document 2 disclose the R—Fe—B based magnet made by sintering and that made by high speed quenching, respectively. However, these kinds of rare earth magnets contain rare earth elements, which are relatively easily oxidized, as main components resulting in very low anticorrosion property. Problems caused by this are that a magnetic performance decreases at manufacturing and use and/or that reliability of a manufactured magnet is relatively low, and so on. In order to improve such anticorrosion property of rare earth magnets, for example, as described on patent document 3 to 10, a proposal has been made to form a variety of protecting films on the surface of such magnets, so far.
More specifically, with the purpose of improving antioxidation property of the permanent magnet containing rare earths, boron, and iron as main components, patent document 3, for example, proposes the permanent magnet made by covering an antioxidation plated layer over the surface of a permanent magnet body, which contains R (where, R is at least 1 species of rare earth elements) 8 atom percents to 30 atom percents, B 2 atom percents to 28 atom percents, and Fe 4 atom percents to 90 atom percents as main components and has a main phase composed of the tetragonal crystalline phase. This patent document 3 discloses plating a metal Ni, Cu, Zn, and the like or an alloy, that has the anti-oxidizing property, or composite plating composed thereof.
On the other hand, patent document 4 discloses a method of forming the resin-made protecting layer having a thickness ranging from 5 to 25 μm on the surface of a magnet body.
[Patent document 1] Japanese Published Unexamined Patent Application No. SHO 59-46008
[Patent document 2] Japanese Published Unexamined Patent Application No. SHO 60-9852
[Patent document 3] Japanese Published Unexamined Patent Application No. SHO 60-54406
[Patent document 4] Japanese Published Unexamined Patent Application No. SHO 60-63901
[Patent document 5] Japanese Published Unexamined Patent Application No. SHO 60-63902
[Patent document 6] Japanese Published Unexamined Patent Application No. SHO 61-130453
[Patent document 7] Japanese Published Unexamined Patent Application No. SHO 61-166115
[Patent document 8] Japanese Published Unexamined Patent Application No. SHO 61-166116
[Patent document 9] Japanese Published Unexamined Patent Application No. SHO 61-270308